Functional correlates of auditory structures in the brainstem and periphery will be studied. Experiments in the brainstem will examine the discharge characteristics of single units in the lateral superior olive (LSO) of unanesthetized cats. After producing an ischemic decerebration, one of two experimental paradigms will be followed: 1) either the neuronal response to dichotic transient sounds will be explored, or 2) the nature of the ipsilateral inputs will be examined by functionally isolating the LSO from its contralateral input. These experiments will attack the general neurophysiological problems of excitatory-inhibitory interactions as well as the more specific functions the LSO serves in the analysis of binaural hearing, particularly its role in detection of the short interaural-time differences involved in localization of transients. A second experiment will examine synaptic activity of receptor cells of the guinea pig organ of Corti. Micropinocytotic uptake of the enzyme horseradish peroxidase (HRP) will be utilized to investigate stimulus dependent changes in synaptic activity in the inner and outer hair cells. After HRP has been introduced into the perilymph, its uptake will be assessed by light and electron microscopic techniques. Clarification of synaptic interactions in the cochlea may contribute to an understanding of the etiology of sensorineural hearing loss.